Cynthia Eid

Iron-based 1D nanostructures by electrospinning process

Iron-based 1D nanostructures have been successfully prepared using an electrospinning technique and varying the pyrolysis atmospheres. Hematite (Fe(2)O(3)) nanotubes and polycrystalline Fe(3)C nanofibers were obtained by simple air or mixed gas (H(2), Ar) annealing treatments. Using the air annealing treatment, a high control of the morphology as well as of the wall thickness of the nanotubes was demonstrated with a direct influence of the starting polymer concentration. When mixed gases (H(2) and Ar) were used for the annealing treatments, for the first time polycrystalline Fe(3)C nanofibers composed of carbon graphitic planes were obtained, ensuring Fe(3)C nanoparticle stability and nanofiber cohesion. The morphology and structural properties of all these iron-based 1D nanostructures were fully characterized by SEM, TEM, XRD and Raman spectroscopy.

Enhanced photocatalytic performance of novel electrospun BN/TiO2 composite nanofibers

High activity boron nitride/titanium dioxide (BN/TiO2) composite nanofiber photocatalysts were synthesized for the first time via the electrospinning technique. The as-spun nanofibers with a controlled ratio of boron nitride nanosheets (BN) were calcined under air at 500 °C for 4 hours. Their morphological, structural and optical properties were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), BET surface area, Fourier-transform infrared (FTIR), Raman spectroscopy, UV-Visible spectrophotometry and room temperature photoluminescence (PL). The effect of loading different BN sheet amounts on the photocatalytic degradation of methyl orange (MO) was investigated. The results indicated that the presence of BN sheets improved the separation of the photo-induced electron–hole pairs in TiO2 and increased the band gap energy and the specific surface area compared to pure TiO2 nanofibers. BN/TiO2 (10 wt%) composite nanofiber photocatalytic activity is enhanced to 99% compared to 60% and 65% for P25 and TiO2 nanofibers, respectively. Thus, the BN/TiO2 composites significantly increase the UV light photo-response and improve the separation of photo-induced electron–hole pairs of TiO2.

Synthesis of novel ZnO/ZnAl2O4 multi co-centric nanotubes and their long-term stability in photocatalytic application

Based on the Kirkendall effect, novel double, triple and quadruple co-centric nanotubes of ZnO/ZnAl2O4 have been successfully fabricated by combining the two techniques of electrospinning and atomic layer deposition. The as-prepared samples were annealed at 900 °C under air. Their morphological, structural and optical properties were studied by Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), UV-visible spectrophotometry, Raman spectroscopy, photoluminescence (PL) and reflectance emission. The performances and long-term stability of these multi co-centric nanotubes for photocatalytic applications have been evaluated under the same conditions. As result, in the photodegradation of methyl orange (MO) under UV irradiation, the triple and quadruple co-centric nanotubes of ZnO/ZnAl2O4 exhibit a higher photodegradation efficiency (94% and 99%, respectively) in repeated and long-term applications compared to the pure ZnO which has very low long-term photocatalytic stability. Thus, the fact of coupling these two semiconductors ensured a high photocatalytic activity and long term stability.

Tunable properties of GO-doped CoFe2O4 nanofibers elaborated by electrospinning

Cobalt ferrite (CoFe2O4) one-dimensional nanofibers doped with graphene oxide (GO) were successfully synthesized for the first time via an electrospinning technique. The as-spun nanofibers were calcined at 600 °C for 3 h with a slow heating rate of 2 °C min−1. Their morphological and structural properties were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy, energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy. All GO-doped CoFe2O4 fibers possessed a pure spinel structure. The average fiber diameter and grain size were influenced by the GO weight amount. The effect of the graphene oxide incorporation on the magnetic properties of the fibers was investigated by superconducting quantum interference device (SQUID) magnetometry. At room temperature, a slight enhancement of the saturation magnetization was detected while increasing the GO amount. Therefore, doping with GO is able to tune the magnetic properties of the CoFe2O4 fibers elaborated by the electrospinning technique.

High photodegradation and antibacterial activity of BN–Ag/TiO2 composite nanofibers under visible light

To develop material with good photocatalytic properties for organic compound degradation and bacterial removal, we produced Ag/TiO2 and BN–Ag/TiO2 composite nanofibers that included controlled amounts of boron nitride (BN) nanosheets and silver (Ag). After annealing at 500 °C under air, we used scanning electron microscopy, transmission electron microscopy, Brunauer–Emmet–Teller analysis, X-ray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, UV-visible reflectance spectroscopy and room temperature photoluminescence to investigate the morphological, structural and optical properties of all samples. The photocatalytic tests using methylene blue under visible light, in repeated and long-term applications, showed that the photodegradation activity of BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers was 17.2 and 2.3 times higher than that of pure TiO2 and Ag(3 wt%)/TiO2 nanofibers, respectively. In antibacterial tests using Gram-negative Escherichia coli, 3 hours of incubation with BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers killed all bacteria. These results indicate that the synthesized BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers can be considered to be a multifunctional material for photodegradation and antibacterial applications.

Synthesis and Characterization of Advanced Carbon-Based Nanowires – Study of Composites Actuation Capabilities Containing These Nanowires as Fillers

Electromechanical properties in polymers can be employed to create a large number of sen‐ sors and actuators [1-2]. For example they could replace the piezoelectric materials common‐ ly used in Micro Electromechanical Systems (MEMS). Even if the electromechanical coupling is relatively weak for polymers, they can generate high strains due to electrostric‐ tive and Maxwell effects which are a quadratic function of the applied electric field as op‐ posed to a linear function for piezoelectric materials. Other advantages of the polymers are their ease of processability, flexibility and cheapness.

Hyper frequency modeling of resonated systems based on piezoelectric LiTaO 3 thin layers

In this work, we discuss the piezoelectric activity of lithium tantalite (LiTaO3) thin layers and to more understand this phenomenon we have developed a model for our LiTaO3 resonators based on mason model and simulated the hyper frequency behavior. Our LiTaO3 resonators are made from three layers staked on silicon substrates. The aluminum thin film constitutes the external electrode, the platinum forms the internal electrode and the lithium tantalite constitutes the piezoelectric layer. Each element of these layers is represented by an arrangement of impedances. The simulation shows the reflection coefficient, ρ, as a function of the frequency. We observe a resonant frequency that decreases with the increase of the thickness of the piezoelectric LiTaO3 layers. A slight variation of this resonant frequency is obtained when comparing it with that of the uncharged piezoelectric device, which is due to the different layers loading the system. Over oscillations superposing to the envelope are observed and found to be related to the propagation of the acoustic wave in the silicon substrate. From these over oscillations one can see that this system can be used as an efficient method to calculate the thickness of any substrate.